The present invention relates to a wireless communication system, and more particularly, to a receiver receiving target signals complying with a specific wireless communication specification comprising a specific spectrum characteristic, and a receiving method thereof.
In a wireless local area network (WLAN) system, multiple carriers share a frequency band, and each carrier occupies a sub-band (i.e. a channel) of the frequency band for signal transmission. In general, carriers are put as far away from each other as possible by channel planning in order to avoid adjacent channel interference. However, because the amount of carriers in a frequency band has increased rapidly due to the growth of wireless apparatus, carriers being arranged closely in the frequency band is unavoidable (for example, a neighbor channel may only be ±5 MHz from a target channel), causing signal overlaps at the receiving end.
In order to reduce the effects of adjacent channel interference or adjacent interference sources (such as probe requests sent by devices in the adjacent band), a traditional receiver 100 is designed to have the architecture shown in FIG. 1. When receiving signals, the traditional receiver 100 initially down converts a received signal to base band and extracts a packet of the received signal through a packet detection unit 110. After an automatic gain controller (AGC) 120 locks the packet, a signal quality detecting unit 130 detects the packet, which is usually a preamble packet or a packet of training sequences of the received signal, to check whether the received signal is a desired in-band signal (i.e. a signal in the same channel used for transmitting desired data). When the received signal is detected as the in-band signal, the following blocks in the receiver 100 proceed to obtain the data carried in the received signal. If the signal quality detecting unit 130 determines that the received signal is not the in-band signal, however, the receiver 100 discards the received signal and restarts to detect a next incoming signal.
As can be seen, a main function of the signal quality detecting unit 130 is to quickly and correctly differentiate desired in-band signals from out-of-band signals that overlap into the target receiving channel of the receiver 100. If the signal quality detecting unit 130 mistakes the out-of-band signal as the in-band signal, a false alarm occurs. The data decoded by the receiver 100 is incorrect in this situation, and even if the error is detected by the decoder later, power is consumed and a time loss is formed. The faster the out-of-band signal is distinguished by the signal quality detecting unit 130, the sooner the receiver 100 can restart to prepare for detecting the next incoming signal, and therefore there is a lower packet miss rate.
Common techniques utilized by the signal quality detecting unit 130 for detecting in-band signals are auto-correlation and cross-correlation, which are standard methods of estimating the degree to which two series are correlated in the time domain. However, efficiency of the signal quality detecting unit 130 adopting auto-correlation or cross-correlation may not be acceptable when the channel condition is severe. This is because the in-band signal may be distorted by inter-symbol-interference (ISI) caused by severe multi-path channels. Further, the correlation strength of the in-band signal derived by the signal quality detecting unit 130 becomes weaker due to interferences so that the signal quality detecting unit 130 cannot correctly distinguish the in-band signal from interference noise.